class Dog():
    def __init__(self,name, age):
        self.name = name
        self.age = age
    def sit(self):
        print(f"{self.name} is now sitting.")
    def roll_over(self):
        print(f"{self.name} rolled over!")
my_dog = Dog('willie', 6)
print(f"My dog's name is {my_dog.name}.")
print(f"My dog is {my_dog.age} years old.")